Method of measuring measurement target

ABSTRACT

In order to measure a measurement target on a PCB, height information of the PCB is acquired by using a first image photographed by illuminating a grating pattern light onto the PCB. Then, a first area protruding on the PCB by greater than a reference height is determined as the measurement target by using the height information. Thereafter, color information of the PCB is acquired by using a second image photographed by illuminating light onto the PCB. Then, the first color information of the first area determined as the measurement target out of the color information of the PCB is set as reference color information. Thereafter, the reference color information is compared with color information of an area except for the first area to judge whether the measurement target is formed in the area except for the first area. Thus, the measurement target may be accurately measured.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from and the benefit of Korean PatentApplications No. 2009-41514 filed on May 13, 2009, No. 2010-34057 filedon Apr. 14, 2010, and No. 2010-43731 filed on May 11, 2010, which arehereby incorporated by reference for all purposes as if fully set forthherein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Exemplary embodiments of the present invention relate to a method ofmeasuring a measurement target. More particularly, exemplary embodimentsof the present invention relate to a method of measuring a measurementtarget capable of enhancing accuracy.

2. Discussion of the Background

Generally, at least one printed circuit board (PCB) is employed in anelectronic device. The PCB typically includes a base board, a connectionpad part, and a driver chip electrically connected to the connection padpart.

A connection terminal is disposed beneath the driver chip to beelectrically connected to the connection pad part, and the connectionterminal is typically electrically connected to the connection pad partvia solder formed on the connection pad part. Thus, a method ofmanufacturing the PCB necessarily includes forming the solder on theconnection pad part.

An amount of the solder formed on the connection pad part may have aneffect on electrical connection between the connection pad part and theconnection terminal. That is, when the solder is formed too much,shorting defect may be generated between adjacent connection pad parts,and when the solder is formed relatively little, electrical badconnection may be generated between the connection pad part and theconnection terminal.

As described above, since the amount of the solder formed on theconnection pad part may have a great effect on electrical connectionbetween the connection pad part and the connection terminal, a processof accurately measuring a volume of the solder formed on the PCB isrequired.

SUMMARY OF THE INVENTION

Exemplary embodiments of the present invention provide a method ofmeasuring a measurement target capable of accurately measuring an areaof the measurement target.

Exemplary embodiments of the present invention also provide a method ofmeasuring a solder area capable of accurately measuring an area ofsolder formed on a printed circuit board.

Exemplary embodiments of the present invention also provide a method ofcorrecting uniformity for each color before measuring a solder area foreach color to increase accuracy of measuring the solder area.

Additional features of the invention will be set forth in thedescription which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention.

An exemplary embodiment of the present invention discloses a method ofmeasuring a measurement target on a printed circuit board (PCB). Themethod includes acquiring a three dimensional height information of thePCB by using a first image that is photographed by illuminating agrating pattern light using a first illumination unit onto the PCB,determining a first area protruding on the PCB by a height greater thanor equal to a reference height as a measurement target by using theacquired height information, acquiring a color information of the PCB byusing a second image that is photographed by illuminating a lightgenerated from a second illumination unit onto the PCB, setting thefirst color information of the first area that is determined as themeasurement target out of the acquired color information of the PCB as areference color information, and comparing the reference colorinformation with a color information of an area except for the firstarea to judge whether the measurement target is formed or not in thearea except for the first area.

The method may further include classifying the reference colorinformation of the first area and the color information of the areaexcept for the first area into first and second clusters. Comparing thereference color information with the color information of the areaexcept for the first area to judge whether the measurement target isformed or not in the area except for the first area may include checkingwhether the second cluster belongs to the first cluster or not, and incase that the second cluster belongs the first cluster, judging that anarea corresponding to the second cluster belongs to the measurementtarget area.

The first and second clusters may include a feature extracted from theacquired color information by using a color coordinate system, and thefeature includes at least one of hue, saturation, and intensity.

The method may further include acquiring a second color information of asecond area, in which a predetermined comparison object is located toprotrude on the PCB, from the measured color information of the PCB,acquiring a third color information of a third area, in which themeasurement target is not formed, from the measured color information ofthe PCB, and classifying the first, second and third color informationsof the first, second and third areas into first, second and thirdclusters, respectively, Comparing the reference color information withthe color information of the area except for the first area to judgewhether the measurement target is formed or not in the area except forthe first area may include checking whether a color information of apredetermined portion on the PCB except for the first, second and thirdareas belongs to the first cluster, and in case that the colorinformation belongs to the first cluster, judging that the measurementtarget is formed on the predetermined portion.

The method may further include acquiring a visibility information basedon N grating pattern lights according to movement of a grating unit, andcomparing a visibility information of the first area and a visibilityinformation of an area except for the first area to judge whether themeasurement target is formed or not in the area except for the firstarea.

Another exemplary embodiment of the present invention discloses a methodof measuring a measurement target on a PCB. The method includesacquiring a three dimensional height information and a visibilityinformation of the PCB by using a first image that is photographed byilluminating a grating pattern light using a first illumination unitonto the PCB, determining a first area protruding on the PCB by a heightgreater than or equal to a reference height as a measurement target byusing the acquired height information, and comparing a first visibilityinformation of the first area with a second visibility information of anarea except for the first area to judge whether the measurement targetis formed or not in the area except for the first area.

Still another exemplary embodiment of the present invention discloses amethod of measuring a solder area. The method includes illuminating aplurality of color illuminations onto a PCB to acquire a plurality ofcolor images, generating a saturation map by using the acquired colorimages, and extracting a solder area by using the saturation map.

Illuminating the color illuminations onto the PCB to acquire the colorimages may include illuminating a red illumination, a green illuminationand a blue illumination to acquire a red image, a green image and a blueimage, respectively.

Generating the saturation map by using the acquired color images mayinclude acquiring at least one of hue information, saturationinformation and intensity information for each color through a colorcoordinate conversion of the color images, and generating the saturationmap by using the saturation information for each color.

Extracting the solder area by using the saturation map may includeexcluding at least one of a wiring pattern area and a dark solder resistarea from the saturation map by using the intensity information for eachcolor and setting the solder area.

Extracting the solder area by using the saturation map may includeproducing a saturation average for each color in the solder area,generating a variance map by using the saturation information for eachcolor and the saturation average for each color, and comparing avariance value in the variance map with a critical value to generate asolder map representing the solder area in which a solder is formed.Each of the variance values for pixels may be acquired by the equation,“variance value for each pixel=abs(R−RA)+abs(G−GA)+abs(B−BA)”. ‘IR’, ‘G’and ‘B’ are saturation informations for each pixel, and ‘RA’, ‘GA’ and‘BA’ are saturation averages for each color.

Before illuminating the color illuminations onto the PCB to acquire thecolor images, the method may include illuminating the colorilluminations onto a target to acquire a plurality of illuminationimages for colors, obtaining an intensity for each pixel with respect toeach of the illumination images for colors, and setting a compensationratio for each color, corresponding to a ratio between the intensity foreach pixel and an arbitrary reference intensity, for each pixel. Beforegenerating the saturation map by using the acquired color images, themethod may include compensating for the color images by using thecompensation ratio for each color. The reference intensity maycorrespond to an average intensity of each of the color images.

Before illuminating the color illuminations onto the PCB to acquire thecolor images, the method may include illuminating the colorilluminations onto a solder formed on the PCB to acquire a plurality ofsolder images for each color, obtaining an intensity for each color ofthe solder from each of the solder images for each color, and setting acompensation ratio for each color of the solder, corresponding to aratio between the intensity for each color of the solder and anarbitrary reference intensity. Before generating the saturation map byusing the acquired color images, the method may include compensating forthe color images by using the compensation ratio for each color of thesolder. The reference intensity may correspond to an average intensityof a plurality of solder intensities for each color.

Before illuminating the color illuminations onto the PCB to acquire thecolor images, the method may include setting a compensation ratio foreach color of the color illuminations to correct color uniformity forthe color illuminations, and setting a compensation ratio for each colorof a solder to correct solder uniformity for the color illuminations.Before generating the saturation map by using the acquired color images,the method may include multiplying each color image by the compensationratio for each color of the color illuminations and the compensationratio for each color of the solder.

According to the above, an area corresponding to a height greater thanor equal to a predetermined reference height H1 is determined as asolder area, and a color information of the solder area is set as areference color information to compare the color information of thesolder area with other area. Thus, an area corresponding to a heightbelow the reference height H1, which may be omitted, is incorporated inthe solder area, to thereby accurately measure the solder area.

In addition, even though solder is spread thin on the base board, whichoften generates in forming solder, the solder area may be measured withaccuracy.

In addition, when the color information of the first area AR1, a solderarea corresponding to a height greater than or equal to a predeterminedreference height H1 and the color information of the second and thirdareas AR2 and AR3 are acquired and clustered, a portion not clear toincorporate in the solder area may be more clearly judged.

In addition, a solder area may be more accurately determined by using avisibility information.

In addition, a solder area may be more accurately determined byilluminating grating pattern lights in various directions.

In addition, a shape is three dimensionally measured and an area is twodimensionally judged with accuracy, and an area may be threedimensionally and two dimensionally determined in real-time, so thateffects according to equipments such as illuminations or a condition ofa PCB may be reduced, and robustness for noise may be attained.

In addition, the saturation map and the variance map are generated byusing the color images obtained through the color illuminations, and thesolder area is set by using the saturation map and the variance map,thereby increasing accuracy of measuring the solder area. In addition,before measuring the solder area, at least one process of correcting thecolor uniformity for the color illuminations and correcting the solderuniformity for the color illuminations is performed, thereby enhancingaccuracy of measuring the solder area.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention, andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is a schematic view illustrating a three dimensional shapemeasurement apparatus used to a method of measuring a three dimensionalshape according to an exemplary embodiment of the present invention.

FIG. 2 is a flow chart showing a method of measuring a solder areaaccording to an exemplary embodiment of the present invention.

FIG. 3 is a cross-sectional view illustrating a portion of a PCB onwhich a solder is formed.

FIG. 4 is a flow chart showing an exemplary embodiment of a process ofacquiring two dimensional color information included in the method ofmeasuring the solder area in FIG. 2.

FIG. 5 is a flow chart showing a method of measuring a solder areaaccording to another exemplary embodiment of the present invention.

FIG. 6 is a schematic view illustrating a three dimensional shapemeasurement apparatus used to a method of measuring a three dimensionalshape according to another exemplary embodiment of the presentinvention.

FIG. 7 is a flow chart showing a method of measuring a solder areaaccording to still another exemplary embodiment of the presentinvention.

FIG. 8 shows a red image, a green image and a blue image correspondingto a red illumination, a green illumination and a blue illumination,respectively.

FIG. 9 is an image showing an example of a saturation map.

FIG. 10 is an image showing an example of a variance map.

FIG. 11 is an image showing an example of a solder map.

FIG. 12 is a flow chart showing a method of correcting color uniformityaccording to an exemplary embodiment of the present invention.

FIG. 13 is an image showing a red illumination acquired by employing agray target as a target object.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The present invention is described more fully hereinafter with referenceto the accompanying drawings, in which example embodiments of thepresent invention are shown. The present invention may, however, beembodied in many different forms and should not be construed as limitedto the example embodiments set forth herein. Rather, these exampleembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the present invention tothose skilled in the art. In the drawings, the sizes and relative sizesof layers and regions may be exaggerated for clarity.

It will be understood that when an element or layer is referred to asbeing “on,” “connected to” or “coupled to” another element or layer, itcan be directly on, connected or coupled to the other element or layeror intervening elements or layers may be present. In contrast, when anelement is referred to as being “directly on,” “directly connected to”or “directly coupled to” another element or layer, there are nointervening elements or layers present. Like numerals refer to likeelements throughout. As used herein, the term “and/or” includes any andall combinations of one or more of the associated listed items.

It will be understood that, although the terms first, second, third etc.may be used herein to describe various elements, components, regions,layers and/or sections, these elements, components, regions, layersand/or sections should not be limited by these terms. These terms areonly used to distinguish one element, component, region, layer orsection from another region, layer or section. Thus, a first element,component, region, layer or section discussed below could be termed asecond element, component, region, layer or section without departingfrom the teachings of the present invention.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the exemplary term “below” can encompass both anorientation of above and below. The device may be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting of thepresent invention. As used herein, the singular forms “a,” “an” and“the” are intended to include the plural forms as well, unless thecontext clearly indicates otherwise. It will be further understood thatthe terms “comprises” and/or “comprising,” when used in thisspecification, specify the presence of stated features, integers, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof.

Example embodiments of the invention are described herein with referenceto cross-sectional illustrations that are schematic illustrations ofidealized example embodiments (and intermediate structures) of thepresent invention. As such, variations from the shapes of theillustrations as a result, for example, of manufacturing techniquesand/or tolerances, are to be expected. Thus, example embodiments of thepresent invention should not be construed as limited to the particularshapes of regions illustrated herein but are to include deviations inshapes that result, for example, from manufacturing. For example, animplanted region illustrated as a rectangle will, typically, haverounded or curved features and/or a gradient of implant concentration atits edges rather than a binary change from implanted to non-implantedregion. Likewise, a buried region formed by implantation may result insome implantation in the region between the buried region and thesurface through which the implantation takes place. Thus, the regionsillustrated in the figures are schematic in nature and their shapes arenot intended to illustrate the actual shape of a region of a device andare not intended to limit the scope of the present invention.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

Hereinafter, exemplary embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.

FIG. 1 is a schematic view illustrating a three dimensional shapemeasurement apparatus used to a method of measuring a three dimensionalshape according to an exemplary embodiment of the present invention.

Referring to FIG. 1, a three dimensional shape measurement apparatusused to a method of measuring a three dimensional shape according to anexemplary embodiment of the present invention may include a measurementstage section 100, an image photographing section 200, a firstillumination unit including first and second illumination sections 300and 400, a second illumination unit 450, an image acquiring section 500,a module control section 600 and a central control section 700.

The measurement stage section 100 may include a stage 110 supporting ameasurement target 10 and a stage transfer unit 120 transferring thestage 110. In an exemplary embodiment, according as the measurementtarget 10 moves with respect to the image photographing section 200 andthe first and second illumination sections 300 and 400 by the stage 110,a measurement location may be changed in the measurement target 10.

The image photographing section 200 is disposed over the stage 110 toreceive light reflected by the measurement target 10 and measure animage of the measurement target 10. That is, the image photographingsection 200 receives the light that exits the first and secondillumination sections 300 and 400 and is reflected by the measurementtarget 10, and photographs a plan image of the measurement target 10.

The image photographing section 200 may include a camera 210, an imaginglens 220, a filter 230 and a lamp 240. The camera 210 receives the lightreflected by the measurement target 10 and photographs the plan image ofthe measurement target 10. The camera 210 may include, for example, oneof a CCD camera and a CMOS camera. The imaging lens 220 is disposedunder the camera 210 to image the light reflected by the measurementtarget 10 on the camera 210. The filter 230 is disposed under theimaging lens 220 to filter the light reflected by the measurement target10 and provide the filtered light to the imaging lens 220. The filter230 may include, for example, one of a frequency filter, a color filterand a light intensity control filter. The lamp 240 may be disposed underthe filter 230 in a circular shape to provide the light to themeasurement target 10, so as to photograph a particular image such as atwo-dimensional shape of the measurement target 10.

The first illumination section 300 may be disposed, for example, at aright side of the image photographing section 200 to be inclined withrespect to the stage 110 supporting the measurement target 10. The firstillumination section 300 may include a first light source unit 310, afirst grating unit 320, a first grating transfer unit 330 and a firstcondensing lens 340. The first light source unit 310 may include a lightsource and at least one lens to generate light, and the first gratingunit 320 is disposed under the first light source unit 310 to change thelight generated by the first light source unit 310 into a first gratingpattern light having a grating pattern. The first grating transfer unit330 is connected to the first grating unit 320 to transfer the firstgrating unit 320, and may include, for example, one of a piezoelectrictransfer unit and a fine linear transfer unit. The first condensing lens340 is disposed under the first grating unit 320 to condense the firstgrating pattern light exiting the first grating unit 320 on themeasurement target 10.

For example, the second illumination section 400 may be disposed at aleft side of the image photographing section 200 to be inclined withrespect to the stage 110 supporting the measurement target 10. Thesecond illumination section 400 may include a second light source unit410, a second grating unit 420, a second grating transfer unit 430 and asecond condensing lens 440. The second illumination section 400 issubstantially the same as the first illumination section 300 describedabove, and thus any further description will be omitted.

When the first grating transfer unit 330 sequentially moves the firstgrating unit 320 by N times and N first grating pattern lights areilluminated onto the measurement target 10 in the first illuminationsection 300, the image photographing section 200 may sequentiallyreceive the N first grating pattern lights reflected by the measurementtarget 10 and photograph N first pattern images. In addition, when thesecond grating transfer unit 430 sequentially moves the second gratingunit 420 by N times and N second grating pattern lights are illuminatedonto the measurement target 10 in the second illumination section 400,the image photographing section 200 may sequentially receive the Nsecond grating pattern lights reflected by the measurement target 10 andphotograph N second pattern images. The ‘N’ is a natural number, and forexample may be four.

In an exemplary embodiment, the first and second illumination sections300 and 400 are described as an illumination apparatus generating thefirst and second grating pattern lights. Alternatively, the illuminationsection may be more than or equal to three. In other words, the gratingpattern light may be illuminated onto the measurement target 10 invarious directions, and various pattern images may be photographed. Forexample, when three illumination sections are disposed in an equilateraltriangle form with the image photographing section 200 being the centerof the equilateral triangle form, three grating pattern lights may beilluminated onto the measurement target 10 in different directions. Forexample, when four illumination sections are disposed in a square formwith the image photographing section 200 being the center of the squareform, four grating pattern lights may be illuminated onto themeasurement target 10 in different directions. In addition, the firstillumination unit may include eight illumination sections, and gratingpattern lights may be illuminated onto the measurement target 10 ineight directions to photograph an image.

The second illumination unit 450 illuminates light for acquiring a twodimensional image of the measurement target 10 onto the measurementtarget 10. In an exemplary embodiment, the second illumination unit 450may include a red illumination 452, a green illumination 454, and a blueillumination 456. For example, the red illumination 452, the greenillumination 454, and the blue illumination 456 may be disposed in acircular shape over the measurement target 10 to illuminate a red light,a green light and a blue light, respectively, and may be disposed atdifferent heights as shown in FIG. 1.

The image acquiring section 500 is electrically connected to the camera210 of the image photographing section 200 to acquire the pattern imagesaccording to the first illumination unit from the camera 210 and storethe acquired pattern images. In addition, the image acquiring section500 acquires the two dimensional images according to the secondillumination unit from the camera 210 and store the acquired twodimensional images. For example, the image acquiring section 500 mayinclude an image system that receives the N first pattern images and theN second pattern images photographed in the camera 210 and stores theimages.

The module control section 600 is electrically connected to themeasurement stage section 100, the image photographing section 200, thefirst illumination section 300 and the second illumination section 400,to control the measurement stage section 100, the image photographingsection 200, the first illumination section 300 and the secondillumination section 400. The module control section 600 may include,for example, an illumination controller, a grating controller and astage controller. The illumination controller controls the first andsecond light source units 310 and 410 to generate light, and the gratingcontroller controls the first and second grating transfer units 330 and430 to move the first and second grating units 320 and 420. The stagecontroller controls the stage transfer unit 120 to move the stage 110 inan up-and-down motion and a left-and-right motion.

The central control section 700 is electrically connected to the imageacquiring section 500 and the module control section 600 to control theimage acquiring section 500 and the module control section 600.Particularly, the central control section 700 receives the N firstpattern images and the N second pattern images from the image system ofthe image acquiring section 500 to process the images, so that threedimensional shape of the measurement target may be measured. Inaddition, the central control section 700 may control a illuminationcontroller, a grating controller and a stage controller of the modulecontrol section 600. Thus, the central control section may include animage processing board, a control board and an interface board.

Hereinafter, a method of measuring the measurement target 10 formed on aprinted circuit board by using the above described three dimensionalshape measurement apparatus will be described in detail. It will bedescribed employing a solder as an example of the measurement target 10.

FIG. 2 is a flow chart showing a method of measuring a solder areaaccording to an exemplary embodiment of the present invention. FIG. 3 isa cross-sectional view illustrating a portion of a PCB on which a solderis formed.

Referring to FIGS. 1 to 3, in order to measure a solder area, firstly, athree dimensional height information of the PCB 900 is acquired by usinga first image that is photographed by illuminating a grating patternlight using a first illumination unit onto the PCB 900 in step S1110.For example, the grating pattern light may be illuminated in at leasttwo directions.

The three dimensional height information may be acquired by performing abucket algorithm with respect to the first image that is acquired byilluminating grating pattern lights according to sequential movement byN times of the first and second grating units 320 and 420.

Then, a first area AR1 protruding on a base board 910 of the PCB 900 bya height greater than or equal to a reference height H1 is determined asa solder area by using the acquired height information in step S1120.

When an area corresponding to a height greater than or equal to apredetermined minimum height threshold may be generally regarded as asolder area, the reference height H1 may be set as the predeterminedminimum height threshold. Thereafter, a color information of the PCB 900is acquired by using a second image that is photographed by illuminatinga light generated from a second illumination unit 450 onto the PCB 900in step S1130.

The second illumination unit 450 generates a light for acquiring a twodimensional image of the measurement target 10. In an exemplaryembodiment, the second illumination unit 450 may include a redillumination 452, a green illumination 454 and a blue illumination 456generating a red light, a green light and a blue light, respectively.The second image may be acquired using not only a color camera, but alsoa black and white camera. Thus, the camera 210 as shown in FIG. 1 mayinclude a black and white camera. In another exemplary embodiment, thesecond illumination unit 250 may include an illumination unit of amonochromatic light. The second image may be acquired using a colorcamera, and the camera 210 as shown in FIG. 1 may include a colorcamera.

The color information may include, for example, RGB (red, green andblue) information or CMY (cyan, magenta and yellow) information.Besides, the first color information may include a color informationaccording to other color combination. The first color information may beacquired by a pixel unit of the first area AR1.

Meanwhile, the color information of the PCB 900 may be acquired asfollows.

FIG. 4 is a flow chart showing an exemplary embodiment of a process ofacquiring two dimensional color information included in the method ofmeasuring the solder area in FIG. 2.

Referring to FIG. 4, in order to acquire the color information of thePCB 900, firstly, the light generated from the second illumination unit450 is illuminated onto the PCB 900 to photograph the second image instep S1132.

Then, the RGB information or the CMY information is extracted from thephotographed second image in step S1133. In an exemplary embodiment,after the photographed second image is acquired by the image acquiringsection 500 shown in FIG. 1, the RGB information or the CMY informationmay be extracted by using the image processing board shown in FIG. 1.

Thereafter, the extracted RGB information or CMY information is filteredto acquire the filtered RGB information or CMY information in stepS1134. In an exemplary embodiment, in the image processing board, datadeviating from an average is excluded from the extracted RGB informationor CMY information by a selected criterion, and remaining data exceptthe deviating data is finally determined as the RGB information or theCMY information.

Referring again to FIGS. 1 to 3, then, a first color information of thefirst area AR1 that is determined as a solder area out of the acquiredcolor information of the PCB 900 is set as a reference color informationin step S1140.

Thereafter, the reference color information and a color information ofan area except for the first area AR1 are compared to judge whether thesolder is formed or not in the area except for the first area AR1 instep S1150.

Meanwhile, in order to acquire an area having a color information thatis substantially the same as the reference color information, colorinformation of other areas may be used.

FIG. 5 is a flow chart showing a method of measuring a solder areaaccording to another exemplary embodiment of the present invention.

Referring to FIGS. 3 and 5, after setting the first color information ofthe first area AR1 as the reference color information in step S1140, asecond color information of a second area AR2 in which a predeterminedprotruding comparison object 920 is located is acquired from themeasured color information of the PCB 900 in step S1142. The comparisonobject 920 may correspond to a pad of the PCB.

Since the second color information of the second area AR2 may beacquired from the color information, the second color information may besubstantially the same form as the first color information. The secondcolor information may include an RGB information or a CMY information.Besides, the second color information may include a color informationaccording to other color combination.

Thereafter, a third color information of a third area AR3 in which ameasurement target is not formed is acquired from the measured colorinformation of the PCB 900 in step S1144. The third area AR3 correspondsto a surface area having no height.

Since the third color information of the third area AR3 may be acquiredfrom the color information, the third color information may havesubstantially the same form as the first color information and thesecond color information. For example, the third color information mayinclude an RGB information or a CMY information. Besides, the thirdcolor information may include a color information according to othercolor combination.

Then, the first, second and third color informations of the first,second and third areas AR1, AR2 and AR3 are classified into first,second and third clusters in step S1146.

The first, second and third color informations indicate colorinformation of each area, and the color information shows acharacteristic tendency for each area. Thus, the first, second and thirdcolor informations may form a specific cluster for each area.

The cluster may include a feature extracted from the acquired colorinformation by using a color coordinate system. For example, the first,second and third cluster may include at least one of hue, saturation andintensity (HSI) converted from the RGB information or the CMYinformation. The process of converting the RGB information or the CMYinformation into the HSI information may be performed by usingwell-known methods, and thus any further description will be omitted.

A clustering algorithm may be applied to the first, second and thirdareas AR1, AR2 and AR3 with at least one information of each HSIinformation of the areas, so that the first, second and third areas AR1,AR2 and AR3 may be classified into the first, second and third clusters,respectively.

As described above, after the first, second and third areas AR1, AR2 andAR3 are classified into the clusters according to the color information,in comparing the reference color information and the color informationof the area except for the first area AR1 to judge whether the solder isformed or not in the area except for the first area AR1 in step S1150,it is checked whether a color information of a predetermined portion ofthe PCB 900 except for the first, second and third areas AR1, AR2 andAR3 belongs to the first cluster or not, and in case that the colorinformation belongs to the first cluster, it may be judged that thesolder is formed on the predetermined portion.

In case that a predetermined portion on the base board 910, which doesnot belong to the first, second and third areas AR1, AR2 and AR3,corresponds to an area AR4 of a solder existing below the referenceheight H1 (hereinafter, referred to as “fourth area”), since a colorinformation of the fourth area R4 is similar to the first colorinformation of the first area AR1, the fourth area R4 belongs to a groupthat is the same as the group of the first area AR1 classified into thefirst cluster according to the first color information. That is, thefourth area R4 may be classified into the first cluster, which is likethe first area AR1.

Accordingly, in comparison with a method of judging an area onlycorresponding to a height greater than or equal to a predeterminedreference height as a solder area, an area corresponding to a heightsmaller than the predetermined reference height as a solder area may bealso included in the solder area, so that the solder area may be morecorrectly determined.

Although an example of classifying areas into three clusters isdescribed in FIG. 5, the number of the clusters may be two or greaterthan or equal to four.

For example, when the number of the clusters is four, the solder areamay be determined as follows.

Firstly, a color information of a predetermined area except for thefirst area AR1 determined as the solder area is acquired to classify thereference color information of the first area AR1 and the colorinformation of the predetermined area into first and second clusters,respectively. Then, in comparing the reference color information and thecolor information of the area except for the first area AR1 to judgewhether the solder is formed or not in the area except for the firstarea AR1 in step S1150, it is checked whether the second cluster belongsto the first cluster or not, and in case that the second cluster belongsto the first cluster, it may be judged that the area corresponding tothe second cluster belongs to the solder area.

In acquiring the color information of the PCB 900 in step S1130, avisibility information may be additionally used. The visibilityrepresents a ratio of amplitude B_(i)(x,y) to average A_(i)(x,y) inbrightness signals of an image, and roughly has a tendency to increaseas reflectivity increases. The visibility V_(i)(x,y) is defined asfollows.

V _(i)(x,y)=B _(i)(x,y)/A _(i)(x,y)

The grating pattern light is illuminated onto the PCB 900 in variousdirections to photograph various sorts of pattern images. As shown inFIG. 1, the image acquiring section 500 extracts N brightness degreesI^(i) ₁I^(i) ₂, . . . , I^(i) _(N) at each position i(x,y) in an X-Ycoordinate system from N pattern images photographed in the camera 210,and produces average brightness A_(i)(x,y) and visibility V_(i)(x,y) byusing an N-bucket algorithm.

For example, when N is 3, and N is 4, the visibility may be produced asfollows.

When N is 3, the visibility is produced as follows.

${A_{i}\left( {x,y} \right)} = \frac{I_{1}^{i} + I_{2}^{i} + I_{3}^{i}}{3}$${V_{i}\left( {x,y} \right)} = {\frac{B_{i}}{A_{i}} = \frac{\sqrt{\left( {{2I_{1}^{i}} - I_{2}^{i} - I_{3}^{i}} \right)^{2} + {3\left( {I_{2}^{i} - I_{3}^{i}} \right)^{2}}}}{\left( {I_{1}^{i} + I_{2}^{i} + I_{3}^{i}} \right)}}$

When N is 4, the visibility is produced as follows.

${A_{i}\left( {x,y} \right)} = \frac{I_{1}^{i} + I_{2}^{i} + I_{3}^{i} + I_{4}^{i}}{4}$${V_{i}\left( {x,y} \right)} = {\frac{B_{i}}{A_{i}} = \frac{2\sqrt{\left( {I_{1}^{i} - I_{3}^{i}} \right)^{2} + \left( {I_{2}^{i} - I_{4}^{i}} \right)^{2}}}{\left( {I_{1}^{i} + I_{2}^{i} + I_{3}^{i} + I_{4}^{i}} \right)}}$

The color informations such as the first, second and third colorinformations described above show a characteristic tendency for eacharea, and in addition, the visibility information produced as above alsoshows a characteristic tendency for each area. Thus, in addition to thecolor information, the visibility information may be optionally used tomeasure the solder area. Also, the visibility information only may beused to measure the solder area without the color information.

Particularly, the visibility information may be acquired based on Ngrating pattern lights according to the movement of the grating unit,and then the visibility information for the first area and thevisibility information for the area except for the first area arecompared to judge whether the measurement target is formed or not in thearea except for the first area.

The visibility information of the PCB may be acquired by using the firstimage described in FIG. 2. That is, since the first image includes allthe information for acquiring the visibility information describedabove, the visibility information may be acquired from the first image.

The first, second and third areas AR1, AR2 and AR3 may be classifiedinto the first, second and third clusters, which is described in FIG. 5,by using the acquired visibility information, and thus it may be judgedwhether a predetermined portion of the base board 910 except for thefirst, second and third areas AR1, AR2 and AR3 belongs the first clusteror not.

After determining the solder area as described above, the determinedsolder area may be used in various methods. For example, volume of thearea determined as the solder area is produced, and it may be judgedwhether the PCB on which the solder formed is good or bad by using theproduced volume.

As described above, an area corresponding to a height greater than orequal to a predetermined reference height H1 is determined as a solderarea, and a color information of the solder area is set as a referencecolor information to compare the color information of the solder areawith other area. Thus, an area corresponding to a height below thereference height H1, which may be omitted, is incorporated in the solderarea, to thereby accurately measure the solder area.

In addition, even though solder is spread thin on the base board, whichoften generates in forming solder, the solder area may be measured withaccuracy.

In addition, when the color information of the first area AR1, a solderarea corresponding to a height greater than or equal to a predeterminedreference height H1 and the color information of the second and thirdareas AR2 and AR3 are acquired and clustered, a portion not clear toincorporate in the solder area may be more clearly judged.

In addition, a solder area may be more accurately determined by using avisibility information.

In addition, a solder area may be more accurately determined byilluminating grating pattern lights in various directions.

In addition, a shape is three dimensionally measured and an area is twodimensionally judged with accuracy, and an area may be threedimensionally and two dimensionally determined in real-time, so thateffects according to equipments such as illuminations or a condition ofa PCB may be reduced, and robustness for noise may be attained.

FIG. 6 is a schematic view illustrating a three dimensional shapemeasurement apparatus used to a method of measuring a three dimensionalshape according to another exemplary embodiment of the presentinvention.

Referring to FIG. 6, a three dimensional shape measurement apparatus1100 used to a method of measuring a three dimensional shape accordingto an exemplary embodiment of the present invention may include a stage1120, an image photographing section 1130, a first illumination unit1140, a second illumination unit 1150 and a control section 1160.

The stage 1120 supports a measurement target 1110 such as a PCB, andmoves according to control of the control section 1160 to transfer themeasurement target 1110 to a measurement location. According as themeasurement target 1110 moves with respect to the image photographingsection 1130 and the first illumination unit 1140 by the stage 1120, themeasurement location at the measurement target 1110 may be changed.

The image photographing section 1130 is installed over the stage 1120,and receives light reflected by the measurement target 1110 tophotograph an image of the measurement target 1110. The imagephotographing section 1130 is installed, for example, over the stage1110 in a direction substantially perpendicular to a reference surfaceof the stage 1120.

The image photographing section 1130 may include a camera and an imaginglens to photograph the image of the measurement target 1110. The camerareceives the light reflected by the measurement target 1110 tophotograph the image of the measurement target 1110, and may include,for example, a CCD camera or a CMOS camera. The imaging lens is disposedunder the camera to image the light reflected by the measurement target1110 on the camera.

The image photographing section 1130 receives a light reflected by themeasurement target 1110, onto which a pattern illumination illuminatedfrom a first illumination unit 1140 is incident, and photographs apattern image of the measurement target 1110. In addition, the imagephotographing section 1130 receives a light reflected by the measurementtarget 1110, onto which a color illumination illuminated from a secondillumination unit 1150 is incident, and photographs a color image of themeasurement target 1110.

The first illumination unit 1140 is installed over the stage 1120 to beinclined with respect to the stage 1120 by a predetermined angle. Thefirst illumination unit 1140 is for measuring a three dimensional shapeof the measurement target 1110, and generates a pattern illumination toilluminate the measurement target 1110. For example, the firstillumination unit 1140 illuminates the pattern illumination inclined byabout 30 degrees with respect to a normal line of the reference surfaceof the stage 1120.

In order to increase measurement accuracy, the first illumination unit1140 may be plural to illuminate the pattern illumination in variousdirections. A plurality of first illumination units 1140 may be disposedalong a circumferential direction at substantially the same angle basedon the center of the image photographing section 1130. For example, thethree dimensional shape measurement apparatus 1100 may include six firstillumination units 1140 spaced apart at about 60 degrees. Alternatively,the three dimensional shape measurement apparatus 1100 may include firstillumination units 1140 of various numbers such as 2, 3, 4, 8, etc. Thefirst illumination units 1140 illuminate the pattern illumination indifferent directions with respect to the measurement target 1110 atsubstantially the same time interval.

Each first illumination unit 1140 may include a light source 1142 and agrating element 1144 to generate the pattern illumination. Theillumination generated from the light source 1142 is converted into thepattern illumination while passing through the grating element 1144. Thegrating element 1144 moves n times by 2π/n by using a grating transferunit such as a piezoelectric (PZT) actuator to generate the phasetransited pattern illumination. The “n” is a natural number of greaterthan or equal to 2. The first illumination unit 1140 illuminates thepattern illumination onto the measurement target 1110 for each movementwhile moving the grating element 1144 by n times. The first illuminationunit 1140 may further include a projection lens (not shown) to focus thepattern illumination formed by the grating element 1144 and project thefocused pattern illumination onto the measurement target 1110.

The second illumination unit 1150 is for acquiring a two dimensionalimage of the measurement target 1110, and generates and illuminates thecolor illumination onto the measurement target 1110. The secondillumination unit 1150 may include a plurality of color illuminationparts to generate different color illuminations. For example, the secondillumination unit 1150 may include a red illumination part 1152generating a red illumination, a green illumination part 1154 generatinga green illumination and a blue illumination part 1156 generating a blueillumination. The red illumination part 1152, the green illuminationpart 1154 and the blue illumination part 1156 are disposed over themeasurement target 1110 in a circular form to illuminate the redillumination, the green illumination and the blue illumination onto themeasurement target 1110, respectively.

The control section 1160 totally controls the above described elements.Particularly, the control section 1160 controls the movement of thestage 1120 to dispose the measurement target 1110 at the measurementlocation. The control section 1160 operates the first illumination units1140 sequentially. The control section 1160 moves the grating element1144 of each first illumination unit 1140 by pitch and controls thefirst illumination unit 1140 to illuminate the pattern illumination ontothe measurement target 1110 for each movement. The control section 1160controls the second illumination unit 1150 to illuminate the colorillumination onto the measurement target 1110, so as to acquire twodimensional image of the measurement target 1110. The control section1160 controls the image photographing section 1130 to photograph thepattern image acquired by using the pattern illumination that isilluminated from the first illumination unit 1140 and reflected by themeasurement target 1110, and to photograph the color image acquired byusing the color illumination that is illuminated from the secondillumination unit 1150 and reflected by the measurement target 1110. Inaddition, the control section 1160 measures the three dimensional shapeof the measurement target 1110 by using the pattern image and the colorimage photographed in the image photographing section 1130.

Hereinafter, a method of measuring a solder area on a PCB by using thethree dimensional shape measurement apparatus will be described.

FIG. 7 is a flow chart showing a method of measuring a solder areaaccording to still another exemplary embodiment of the presentinvention.

Referring to FIGS. 6 and 7, in order to measure a solder area on a PCB1110, firstly, a plurality of color illuminations is illuminated ontothe PCB 1110 to acquire a plurality of color images in step S1100. Thatis, after sequentially illuminating the color illuminations onto the PCB1110 by using the second illumination unit 1150, the color image isacquired corresponding to each color illumination by using the imagephotographing section 1130. For example, after illuminating a redillumination, a green illumination and a blue illumination onto the PCB1110 by using the red illumination part 1152, the green illuminationpart 1154 and the blue illumination part 1156 included in the secondillumination unit 1150, a red image, a green image and a blue image areacquired corresponding to each color illumination.

FIG. 8 shows a red image, a green image and a blue image correspondingto a red illumination, a green illumination and a blue illumination,respectively.

Referring to FIG. 8, it may be confirmed that distributions of a redimage 1210, a green image 1220 and a blue image 1230 within a field ofview (FOV) are different from each other due to chromatic aberrationaccording to using the red illumination, the green illumination and theblue illumination having different wavelengths,

Then, an HSI information including hue, saturation and intensity foreach color is acquired through the color coordinate conversion of theacquired color images. The process of converting an RGB information intothe HSI information may be performed by using well-known methods, andthus any further description will be omitted.

Before color coordinate converting the acquired color images, thesaturation may be relieved by applying an average filter to the acquiredcolor images.

Thereafter, a saturation map 1300 is generated by using a saturationinformation for each color of the HSI information in step S1110. Anexample of the generated saturation map 1300 is shown in FIG. 9.

The saturation map 1300 may be generated by using the saturationinformation for each pixel with respect to the red image 1210, the greenimage 1220 and the blue image 1230. Particularly, the saturation map1300 may be generated based on the saturation for each pixel produced bythe following Equation 1.

saturation=(11−3*Min(R,G,B)/(R+G+B))   Equation 1

In the Equation 1, ‘IR’ is a saturation information for each pixel inthe red image 1210, ‘G’ is a saturation information for each pixel inthe green image 1220, and ‘B’ is a saturation information for each pixelin the blue image 1230.

The saturation map 1300 generated from the Equation 1 has a range ofabout 0 to about 1, and represents a primary color as the saturation map1300 becomes closer to 1. Since the solder 1310, typically, is close toachromatic color, an area having a value close to 0 in the saturationmap 1300 may be primarily judged as the solder area.

Beside the solder 1310, however, since a wiring pattern 1320, a darksolder resist 1330, etc is also close to achromatic color, an area ofthe wiring pattern 1320, an area of the dark solder resist 1330, etc. inthe saturation map 1300 may be mistaken for the solder area.

Accordingly, after generating the saturation map 1300, an unnecessaryarea such as the wiring pattern 1320, the dark solder resist 1330, etc.may be excluded from the saturation map 1300.

Thus, at least one of the area of wiring pattern 1320 and the area ofthe solder resist 1330 is excluded from the saturation map 1300 by usingthe intensity information for each color of the HSI information to set afirst solder area in step S1120.

The first solder area may be set by using the intensity information outof the HSI information obtained by the color coordinate conversion ofthe color images. Particularly, among the solder 1310, the wiringpattern 1320 and the dark solder resist 1330, there may exist littledifference in view of the saturation, but there may exist muchdifference in view of the intensity. That is, since the wiring pattern1320 including metal has great reflectivity in comparison with thesolder 1310, the intensity of the wiring pattern 1320 is detectedgreater than that of the solder 1310, and since the dark solder resist1330 has little reflectivity in comparison with the solder 1310, theintensity of the dark solder resist 1330 is detected much less than thatof the solder 1310. Thus, an area in which the intensity is great orlittle in comparison with the solder 1310 may be removed by using thedifference of the intensity, to thereby remove the unnecessary area suchas the wiring pattern 1320, the dark solder resist 1330, etc. from thesaturation map 1300.

Then, a saturation average for each color in the first solder area isproduced in step S1130. That is, the saturation average for each coloris produced for each of the red image 1210, the green image 1220 and theblue image 1230 shown in FIG. 8 based on the set first solder area.Since the produced saturation average for each color corresponds to thesaturation average for the first solder area in which it is judged thatthe solder 1310 is substantially formed, the produced saturation averagemay be regarded as a criterion for the saturation of the solder 1310.

Thereafter, a variance map 1400 is generated by using the saturationinformation for each color and the saturation average for each color instep S1140. An example of the generated variance map 1400 is shown inFIG. 10.

The variance map 1400 may be generated by using the saturationinformation for each pixel of the red image 1210, the green image 1220and the blue image 1230 and the saturation average for each color of thered image 1210, the green image 1220 and the blue image 1230.Particularly, the variance map 1400 may be generated based on a variancevalue for each pixel produced by the following Equation 2.

variance=abs(R−RA)+abs(G−GA)+abs(B−BA)   Equation 2

In the Equation 2, ‘R’ is a saturation information for each pixel in thered image 1210, ‘G’ is a saturation information for each pixel in thegreen image 1220, and ‘B’ is a saturation information for each pixel inthe blue image 1230. In addition, ‘RA’ is a saturation average for thefirst solder area in the red image 1210, ‘GA’ is a saturation averagefor the first solder area in the green image 1220, and ‘BA’ is asaturation average for the first solder area in the blue image 1230.

In the Equation 2, as difference between the saturation and thesaturation average of the color image for each pixel become greater, thevariance value of the associated pixel is detected greater, and asdifference between the saturation and the saturation average of thecolor image for each pixel become smaller, the variance value of theassociated pixel is detected smaller. That is, as the variance value foreach pixel is smaller, possibility that the associated pixel correspondsto the solder is greater, and in contrast, as the variance value foreach pixel is greater, possibility that the associated pixel correspondsto the solder is smaller.

Thereafter, the variance values for pixels in the variance map 1400 arecompared to generate a solder map 1500 representing the second solderarea in which the solder is substantially formed in step S1150. Anexample of the generated solder map 1500 is shown in FIG. 11.

A method of setting the second solder area may include setting anarbitrary critical value for the variance value by a user, judging thatthe associated pixel does not correspond to the solder area when thevariance value for the associated pixel exceeds the critical value, andjudging that the associated pixel corresponds to the solder area whenthe variance value for the associated pixel does not exceed the criticalvalue. Meanwhile, in order to set the critical value for the variancevalue, an Otsu algorithm employing a statistical method may be used. TheOtsu algorithm corresponds to a method including setting a cost functionand regarding a value that gives the minimum value of the cost functionas the critical value, in setting the critical value. When a gray valueon an image is classified into two classes, since the distribution ofthe gray value on the image is displayed in a histogram, the criticalvalue corresponds to a discrete level value in the histogram, and aportion below the level value may be classified into class 1 and aportion above the level value may be classified into class 2. Thus,class 1 may be judged as the solder area, and class 2 may be judged asan area that does not belong to the solder area, to thereby set thesecond solder area.

As described above, when the second solder area is set through thecomparison in the variance map 1400, areas except for the solder areasuch as a pattern area may be effectively removed, so that the solderarea may possibly be accurately set. In forming the solder map 1500, thesolder map may be formed more accurately through a process of removing asmall spot, a process of boundary weighting, etc.

Meanwhile, since the second illumination unit 1150 is disposed over thePCB in a circular form to illuminate the color illumination, theintensity may be non-uniformly detected for each area on the color imagephotographed in the image photographing section 1130. Color uniformityfor each color illumination is corrected so as to reduce thenon-uniformity of the intensity for each area, so that reliability formeasuring the solder area may be enhanced.

Correcting the color uniformity for the color illuminations is performedbefore acquiring the color images in FIG. 8, and a compensationinformation for each color for correcting the color uniformity isgenerated through a gray target calibration, and intensity uniformityfor each color may be corrected through the compensation information foreach color.

FIG. 12 is a flow chart showing a method of correcting color uniformityaccording to an exemplary embodiment of the present invention. FIG. 13is an image showing a red illumination acquired by employing a graytarget as a target object.

Referring to FIGS. 6, 12 and 13, in order to correct the coloruniformity, firstly, the color illuminations are illuminated onto a graytarget to acquire a plurality of illumination images for each color instep S1200. That is, after the color illuminations are sequentiallyilluminated onto the gray target by using the second illumination unit1150, the illumination images for colors corresponding to colorilluminations is acquired by using the image photographing section 1130.For example, after the red illumination, the green illumination and theblue illumination are illuminated onto the gray target by using the redillumination part 1152, the green illumination part 1154 and the blueillumination part 1156 included in the second illumination unit 1150, ared illumination image, a green illumination image and blue illuminationimage are acquired corresponding to each color illumination.

For example, referring to FIG. 13 showing the acquired red illuminationimage, it may be confirmed that the intensity varies in locations withinthe field of view (FOV). Then, the intensity for each pixel is obtainedwith respect to the illumination image for each color in step S1210.That is, the intensity information for each pixel is obtained from thered illumination image, the green illumination image and the blueillumination image, and stored.

Thereafter, a compensation ratio for each color, corresponding to aratio between the intensity for each pixel and an arbitrary referenceintensity, is set for each pixel in step S1220. The reference intensitymay be set as an average intensity of the illumination image for eachcolor. For example, an average intensity of total pixels within thefield of view (FOV) of the illumination image for each color is set asthe reference intensity. Alternatively, the reference intensity may beset as an arbitrary value that a user desires. For example, thecompensation ratio for each color with respect to each pixel may beexpressed as Equation 3.

compensation ratio=(average intensity of illumination image for eachcolor)/(intensity of associated pixel)   Equation 3

Then, the compensation ratios for each color of total pixels within thefield of view (FOV) are databased to generate and store the compensationinformation for each color in step S1230. The stored compensationinformation for each color may be used to increase accuracy of measuringthe solder area, which is processed later. For example, after the colorilluminations are illuminated onto the PCB to acquire the color images,before generating the saturation map by using the color images, eachpixel of the color images is compensated for by using the compensationratio for each color. That is, each pixel of the color images ismultiplied by the compensation ratio for each color to compensate forthe intensity non-uniformity of the color illumination itself, andreduce an error of measuring the solder area.

Meanwhile, according to characteristics of a solder ball included in thesolder, deviation of intensity for each color may be generated withinthe solder area. In order to reduce the deviation of the intensity foreach color of the solder, solder uniformity for the color illuminationsmay be corrected to enhance reliability of measuring the solder area.

Correcting the solder uniformity for the color illuminations may beperformed before acquiring the color images shown in FIG. 8.Particularly, the color illuminations are illuminated onto the solderformed on the PCB to acquire solder images for each color. For example,after the red illumination, the green illumination and the blueillumination are illuminated onto the solder formed on the PCB by usingthe red illumination part 1152, the green illumination part 1154 and theblue illumination part 1156 included in the second illumination unit1150, a red solder image, a green solder image and a blue solder imageare acquired corresponding to each color illumination. Thereafter, theintensity for each color of the solder is obtained from each of thesolder images for colors. That is, the intensity for each color of thesolder is obtained from the red solder image, the green solder image andthe blue solder image. The intensity for each color of the solder may beobtained from one pixel corresponding to the solder, or a plurality ofpixels included in a predetermined area of the solder. Then, acompensation ratio for each color of the solder, corresponding to aratio between the intensity for each color of the solder and anarbitrary reference intensity is set, and the set compensation ratio foreach color of the solder is stored. The reference intensity may be setas an average intensity of a plurality of solder intensities for eachcolor. For example, the reference intensity is set as an averageintensity of a red solder intensity obtained from the red solder image,a green solder intensity obtained from the green solder image and a bluesolder intensity obtained from the blue solder image.

The compensation ratio for each color of the solder acquired by theabove described method may be used to increase accuracy of measuring thesolder area, which is processed later. For example, after the colorilluminations are illuminated onto the PCB to acquire the color images,before generating the saturation map by using the color images, thecolor images are compensated for by using the compensation ratio foreach color of the solder. That is, each of the color images ismultiplied by the compensation ratio for each color of the solder tocompensate for the intensity non-uniformity for colors of the solder,and reduce an error of measuring the solder area.

Meanwhile, before acquiring the color images, the compensation ratio foreach color of the color illuminations so as to correct the coloruniformity for the color illuminations and the compensation ratio foreach color of the solder so as to correct the solder uniformity for thecolor illuminations are set by the above described method in advance,and before generating the saturation map, each of the color images ismultiplied by the compensation ratio for each color of the colorillumination and the compensation ratio for each color of the solder, tothereby greatly enhance reliability of measuring the solder area.

As described above, the saturation map and the variance map aregenerated by using the color images obtained through the colorilluminations, and the solder area is set by using the saturation mapand the variance map, thereby increasing accuracy of measuring thesolder area. In addition, before measuring the solder area, at least oneprocess of correcting the color uniformity for the color illuminationsand correcting the solder uniformity for the color illuminations isperformed, thereby enhancing accuracy of measuring the solder area.

It will be apparent to those skilled in the art that variousmodifications and variation can be made in the present invention withoutdeparting from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A method of measuring a measurement target on a printed circuit board(PCB) comprising: acquiring a three dimensional height information ofthe PCB by using a first image that is photographed by illuminating agrating pattern light using a first illumination unit onto the PCB;determining a first area protruding on the PCB by a height greater thanor equal to a reference height as a measurement target by using theacquired height information; acquiring a color information of the PCB byusing a second image that is photographed by illuminating a lightgenerated from a second illumination unit onto the PCB; setting thefirst color information of the first area that is determined as themeasurement target out of the acquired color information of the PCB as areference color information; and comparing the reference colorinformation with a color information of an area except for the firstarea to judge whether the measurement target is formed or not in thearea except for the first area.
 2. The method of claim 1, furthercomprising classifying the reference color information of the first areaand the color information of the area except for the first area intofirst and second clusters, wherein comparing the reference colorinformation with the color information of the area except for the firstarea to judge whether the measurement target is formed or not in thearea except for the first area comprises: checking whether the secondcluster belongs to the first cluster or not; and in case that the secondcluster belongs the first cluster, judging that an area corresponding tothe second cluster belongs to the measurement target area.
 3. The methodof claim 2, wherein the first and second clusters include a featureextracted from the acquired color information by using a colorcoordinate system, and the feature includes at least one of hue,saturation, and intensity.
 4. The method of claim 1, further comprising:acquiring a second color information of a second area, in which apredetermined comparison object is located to protrude on the PCB, fromthe measured color information of the PCB; acquiring a third colorinformation of a third area, in which the measurement target is notformed, from the measured color information of the PCB; and classifyingthe first, second and third color informations of the first, second andthird areas into first, second and third clusters, respectively, whereincomparing the reference color information with the color information ofthe area except for the first area to judge whether the measurementtarget is formed or not in the area except for the first area comprises:checking whether a color information of a predetermined portion on thePCB except for the first, second and third areas belongs to the firstcluster; and in case that the color information belongs to the firstcluster, judging that the measurement target is formed on thepredetermined portion.
 5. The method of claim 1, further comprising:acquiring a visibility information based on N grating pattern lightsaccording to movement of a grating unit; and comparing a visibilityinformation of the first area and a visibility information of an areaexcept for the first area to judge whether the measurement target isformed or not in the area except for the first area.
 6. A method ofmeasuring a measurement target on a PCB comprising: acquiring a threedimensional height information and a visibility information of the PCBby using a first image that is photographed by illuminating a gratingpattern light using a first illumination unit onto the PCB; determininga first area protruding on the PCB by a height greater than or equal toa reference height as a measurement target by using the acquired heightinformation; and comparing a first visibility information of the firstarea with a second visibility information of an area except for thefirst area to judge whether the measurement target is formed or not inthe area except for the first area.
 7. A method of measuring a solderarea comprising: illuminating a plurality of color illuminations onto aPCB to acquire a plurality of color images; generating a saturation mapby using the acquired color images; and extracting a solder area byusing the saturation map.
 8. The method of claim 7, wherein illuminatingthe color illuminations onto the PCB to acquire the color imagescomprising illuminating a red illumination, a green illumination and ablue illumination to acquire a red image, a green image and a blueimage, respectively.
 9. The method of claim 7, wherein generating thesaturation map by using the acquired color images comprising: acquiringat least one of hue information, saturation information and intensityinformation for each color through a color coordinate conversion of thecolor images; and generating the saturation map by using the saturationinformation for each color.
 10. The method of claim 9, whereinextracting the solder area by using the saturation map comprisingexcluding at least one of a wiring pattern area and a dark solder resistarea from the saturation map by using the intensity information for eachcolor and setting the solder area.
 11. The method of claim 9, whereinextracting the solder area by using the saturation map comprising:producing a saturation average for each color in the solder area;generating a variance map by using the saturation information for eachcolor and the saturation average for each color; and comparing avariance value in the variance map with a critical value to generate asolder map representing the solder area in which a solder is formed. 12.The method of claim 11, wherein each of the variance values for pixelsis acquired by the following equation: variance value for eachpixel=abs(R−RA)+abs(G−GA)+abs(B−BA), wherein ‘IR’, ‘G’ and ‘B’ aresaturation informations for each pixel, and ‘RA’, ‘GA’ and ‘BA’ aresaturation averages for each color.
 13. The method of claim 7, prior toilluminating the color illuminations onto the PCB to acquire the colorimages, further comprising: illuminating the color illuminations onto atarget to acquire a plurality of illumination images for colors;obtaining an intensity for each pixel with respect to each of theillumination images for colors; and setting a compensation ratio foreach color, corresponding to a ratio between the intensity for eachpixel and an arbitrary reference intensity, for each pixel, and prior togenerating the saturation map by using the acquired color images,further comprising compensating for the color images by using thecompensation ratio for each color.
 14. The method of claim 13, whereinthe reference intensity corresponds to an average intensity of each ofthe color images.
 15. The method of claim 7, prior to illuminating thecolor illuminations onto the PCB to acquire the color images, furthercomprising: illuminating the color illuminations onto a solder formed onthe PCB to acquire a plurality of solder images for each color;obtaining an intensity for each color of the solder from each of thesolder images for each color; and setting a compensation ratio for eachcolor of the solder, corresponding to a ratio between the intensity foreach color of the solder and an arbitrary reference intensity, and priorto generating the saturation map by using the acquired color images,further comprising compensating for the color images by using thecompensation ratio for each color of the solder.
 16. The method of claim15, wherein the reference intensity corresponds to an average intensityof a plurality of solder intensities for each color.
 17. The method ofclaim 7, prior to illuminating the color illuminations onto the PCB toacquire the color images, further comprising: setting a compensationratio for each color of the color illuminations to correct coloruniformity for the color illuminations; and setting a compensation ratiofor each color of a solder to correct solder uniformity for the colorilluminations, and prior to generating the saturation map by using theacquired color images, further comprising multiplying each color imageby the compensation ratio for each color of the color illuminations andthe compensation ratio for each color of the solder.